The present invention relates to optical recording apparatuses, and more particularly, to optical recording apparatuses that record data on optical storage media.
Optical storage medium, such as DVD discs, is currently a kind of very popular storage medium. For recording data onto an optical disc, the pickup head of an optical disc drive, which is a kind of optical recording apparatus, is used to output laser light with appropriate laser power onto the optical disc. FIG. 1 shows how laser power alternates when data are recoded onto different kinds of optical discs. For a write-once disc, the laser power alternates between a peak power level, a write power level, and a read power level; and if a single mark is going to be established, a single recording pulse will be generated by the laser diode. For a rewritable disc, the laser light power alternates frequently between a write power level, an erase power level, and a bias power level; and if a single mark is going to be established, a plurality of recording pulses (multi pulse) will be generated by the laser diode.
In order to process accurate servo control tasks on the pickup head when recording data on the optical disc, a servo control system of an optical disc drive detects the states of particular signals, such as a focus error signal FE and a tracking error signal TE. Besides, for controlling the laser power at ideal level(s) when recording data on write-once discs (such as CD-R and DVD-R), an automatic power control apparatus (APC) of the optical disc drive is used to detect the real write power and the real read power through a front photodiode output signal FPDO. And for controlling the laser power at ideal level(s) when recording data on rewritable discs (such as CD-RW and DVD-RW), the automatic power control apparatus is used to detect the erase power through the front photodiode output signal FPDO.
Both the previously mentioned servo control process and automatic power control process involve signal status detection. Since the signals alternate frequently as illustrated in FIG. 1, the optical disc drive always uses a sample-and-hold scheme to detect signal status at different power levels. However, considering the restriction on the settling time and sampling speed of the used sampler, and to ensure that the detected signal does not vary too large during the sampling period, signals are sampled only when data patterns (marks or spaces) with run-lengths longer than a length threshold are established. For a low writing speed application, the above-mentioned length threshold is not large, and ordinary frame data is enough for providing data patterns that are long enough for the sampler to sample. Nevertheless, for a high writing speed application, the above-mentioned length threshold becomes larger and ordinary frame data might not be able to provide data patterns that are long enough for the sampler to sample. In this situation, the importance of long run-length sync patterns in frame sync codes becomes more significant.
Taking CD type optical discs (such as CD-R or CD-RW) as an example, there is a frame sync code at the beginning part of each frame. Each frame sync code includes two successive 11T patterns (one is a 11T mark and the other one is a 11T land, both of which can be viewed as a long run-length sync pattern), where T is the length unit of each channel bit. In other words, each frame includes at least one 11T mark and one 11T land, hence there are enough opportunities for the optical disc drive to sample on specific signal(s).
In DVD type optical discs, however, the situation is different. Concerning DVD type optical discs, there are four kinds of recording units, which are “channel bit”, “data frame”, “data sector”, and “error correction code block” (ECC block). Channel bit is the smallest recording unit in optical discs, and normally ‘T’ is used to represent the length of each channel bit. When each byte (containing 8 bits) of data is going to be recorded on an optical disc, eight to fourteen modulation plus (EFM+) will be used to convert 8 bits data into 16 channel bits. The EFM+ restricts that channel bits with the same state (i.e. consecutive marks or consecutive spaces) cannot be shorter than 3T or longer than 11T. In other words, except for frame sync codes, the legal run-lengths of frame data lie between 3T and 11T, run-lengths shorter than 3T or longer than 11T are treated as illegal run-lengths. In the case of frame sync code of DVD type optical discs, different from that of CD type optical disc, each frame sync code contains only one 14T pattern, which could be a 14T mark or a 14T space.
FIG. 2 shows possible data patterns of sync codes in DVD type optical discs. A sync code at the beginning of a frame is determined according the next state of the ending codeword of a previous frame and has two choices, one is primary sync code and the other one is secondary sync code.
When data are recorded onto an optical disc, it is necessary to make the low frequency component as low as possible (or the DC component be as low as possible). Hence, an optical disc drive must continue accumulating a digital sum value (DSV) when data are recorded. For a channel bit ‘1’ being recorded, the DSV is increased by one; and for a channel bit ‘0’ being recorded, the DSV is decreased by one. The DSV should be controlled to be as small as possible. Therefore, each sync code is determined as the primary sync code or the secondary sync code to minimize the DSV. As shown in FIG. 2, at the end of each sync code there is a 22-bit data pattern “0001000000000000010001” (always the same), after a non return to zero invert (NRZI) is applied, the “10000000000000” part of this 22-bit data pattern becomes 14 channel bits with the same state (being a 14T mark or a 14T space), which is referred to as a 14T pattern, and could be viewed as the long run-length sync pattern of DVD type optical discs. The polarity of the 14T pattern in the primary sync code is opposite to that of the 14T pattern in the corresponding secondary sync code. That is, for each pair of a primary sync code and a corresponding secondary sync code, one has the 14T pattern as a mark and the other has the 14T pattern as a space. Moreover, as mentioned before, a sync code is determined to be the primary sync code or the secondary sync code to let the DSV to be minimized.
Aside from determining the type of each 14T pattern according to the DSV minimization principle, United States published application No. 2003/0053389 also discloses an optical disc apparatus that establish a sync pattern of a frame in a plurality of frames to be a mark, and sync pattern(s) of the other frame(s) in the plurality of frames is established as a mark or a space according to the DSV minimization principle.
The scheme disclosed by the United States published application No. 2003/0053389 primarily suits optical disc drives applying a running optimum power control (ROPC), since in the ROPC scheme, the need for sampling on 14T marks is more important than that in automatic power control (APC) scheme. However, in a high writing speed application, the need for sampling on 14T spaces become important too, and this kind of situation is not considered in this published application. In addition, since a sync pattern of a frame in a plurality of frames is fixedly established as a mark, the optical disc drive could not adaptively determine the type of each sync pattern according to the real situation on every time point, hence this published application is not the optimal solution.